This invention relates to an injection molding machine for processing synthetic materials and is of the type which includes an injection molding unit equipped with a changing device for replacing a plasticizing unit forming part of the injection molding unit.
The plasticizing unit--to which the invention is more particularly directed--includes a plasticizing cylinder which has a plurality of independently controllable resistance heaters whose heating wires are supported by ceramic insulating bodies. The resistance heaters are clamped on the outer cylindrical face of the plasticizing cylinder by means of axially split tightening sleeves pressed together by tangentially clamping tightening elements. The plasticizing unit further has handle components for being grasped by conveying means which move the plasticizing unit for effecting replacement. There is further provided a stand on which the plasticizing unit may be set in a stable equilibrium after being separated from the injection molding unit.
A known, automatically replaceable plasticizing unit of the above-outlined type equipped with the usual ceramic heater bodies includes a coupling block which is fixedly connected with the plasticizing cylinder and which includes the plastic material supply channel. The coupling block serves, among others, as the stand for the uncoupled plasticizing unit, as disclosed in European Patent No. 69,221 and German Offenlegungsschrift (non-examined published application) No. 3,229,223. The ceramic heater bodies are of the type disclosed in related brochures by the firms Erge Elektrowarme-technik Franz Messer, D-8563 Schnaltach, Hersbruckerstrasse 31 and Ihne & Tesch, D-5880 Ludenscheid, Am Drostenstuck 18, both of the Federal Republic of Germany.
Further, flat-tube heating bodies are known which find application mostly in industrial electric heating and apparatus construction for heating air and liquid and which are also adapted to perform contact heating. The initially linear flat-tube heater bodies are formed of a cross-sectionally flat tube of chromium nickel steel and heating wires which are embedded within the flat tube in a highly densified magnesium oxide or magnesium silicate material. Such flat-tube heater bodies which are flexible to allow easy bending thereof for adapting them to the specific configurational requirements, may be of the type disclosed in related brochures by the firms Eltra GmbH and Co. KG Leicht & Trambauer Elektrowarmetechnik, P.O.B. 1120, D-6102 Pfungstadt as well as Turk & Hillinger GmbH Elektrowarme, D-7200 Tuttlingen, Friedrichstrasse 21, both of the Federal Republic of Germany. Although such flat-tube heaters have been known and widely used in a great number of environments for decades, including the heating of injection nozzles in injection molding machines (as disclosed in German Utility Model No. 7,345,326), they could not be used in plasticizing cylinders of injection molding machines, one reason having been the problem of protecting the heater wire-free end portions of the heater coils and the connected supply conduits of the plasticizing cylinder against mechanical shocks and impacts externally of the heated zone. Such problems are not encountered in the heating of the less exposed injection nozzles, since their diameter is less than that of the associated plasticizing cylinders.